The present invention is directed to writing instruments and, in particular, to writing instruments having a retraction mechanism for selectively retracting or extending a writing element. More particularly, the present invention relates to a writing instrument with a cam driven retraction mechanism.
Writing instruments are commonly equipped with a retractable writing element. According to one example, a writing instrument may include a press button adapted to control the position of the writing element with respect to the writing instrument barrel. When the press button is pressed toward the writing end of the writing instrument, the writing end of the writing element is forced out of the barrel to allow the writing instrument to be used for writing. After the user is finished writing, the press button may be released, or pressed again, to cause the writing end of the writing element to retract back into the barrel. Repeated use of the writing instrument may cause the mechanism that couples the writing element and the push button to become damaged, thereby causing the writing instrument to work improperly. In addition, the user may inadvertently depress the press button while sliding the writing instrument into a shirt pocket or briefcase, or the press button may be depressed during storage, causing the writing end of the writing element to extend out of the barrel and to create undesired markings on any items, such as the shirt or documents in the briefcase, it may contact.
Another retraction mechanism is a rotating cam or toggle located on the barrel of the writing instrument for controlling the position of the writing element. U.S. Pat. No. 2,896,577 to Merryman et al. describes one example of such a writing instrument, which includes a cam member carried on a fixed pivot at an open end of the barrel, particularly the camming surface. The cam member is exposed to the user and may come into contact with oils, solvents, or other substances that may degrade the materials of the cam member. Also, the open end of the barrel may allow into the barrel dirt, lint, or other contaminants which undesirably affect the operation of the writing instrument. Moreover, the cam member described has a profile with rapid transitions and/or sharp angles that rapidly increase the amount of force the user must apply to the cam member when extending or retracting the writing element, undesirably affecting the perceived feel of the mechanism to the user, and subjecting the cam member and the writing element to high levels of wear.
U.S. Pat. No. 2,988,054 to Yates describes a writing instrument having a pivotless rotating toggle member that cooperates with a bushing to effect retraction and extension of a writing element. The toggle member is located in a cap of the writing instrument and the toggle member and cap have cooperating bearing surfaces that allow respective rotation between the two parts. A lever arm is attached to the bearing surface of the toggle member and extends through a slot in the cap and away from the barrel, and allows the user to manipulate the toggle member. As with the Merryman patent described above, the slot in the cap may allow dirt, lint, or other contaminants into the barrel, which may cause excessive wear between the cooperating bearing surfaces. Moreover, as with the Merryman patent, the toggle has sharply angled transitions that require the user to apply a large force to the lever arm to cause extension and retraction of the writing element, thus increasing the amount of wear on the toggle member and increasing the chances of breaking the lever arm off of the toggle member. Finally, although the construction permits access to the interior, for example to replace the writing element, upon removal of the cap from the barrel, the toggle and bushing may fall but of the cap, thus complicating assembly, and may even become lost.
U.S. Pat. No. 4,917,519 to White et al. discloses a writing instrument having a retraction mechanism that comprises a rotatable wheel eccentrically mounted on an open end of the barrel, and an ink reservoir that snaps into the wheel. The user contacts a radial protrusion on the wheel to retract and to extend the ink reservoir. Similar to the writing instrument of the Merryman patent, oils, solvents, or other substances may come into contact with and degrade the wheel materials, and the open end of the barrel may allow dirt, lint, or other contaminants to enter into the barrel, with a consequent undesirable effect on the operation of the writing instrument. The ink reservoir has opposed projections formed on an end portion thereof that snap fit into complementary recesses in the wheel, thus requiring a special ink reservoir to be used with the writing instrument and increasing the difficulty of replacing the ink reservoir.
U.S. Pat. No. 5,651,626 to Chen describes a writing instrument including a barrel with a rotatable pressure member externally located at one end of the barrel. The pressure member interacts with a spring-loaded cam follower that is mounted around an external surface of the barrel and extends or retracts the ink refill. A finger strip extends away from the pressure member and provides a surface for the user to grasp to rotate the pressure member to extend or to retract a writing element from the barrel. The user may inadvertently contact the finger strip while writing and retract the writing element, or even worse, cause the finger strip to break off of the pressure member.
Thus, there remains a need for a cam-operated writing element retraction mechanism that is durable, is resistant to dirt and other contaminants, provides smooth and easy operation, is comfortable and unobtrusive to hold, and is aesthetically pleasing and fun to use.
The present invention is directed to a writing instrument with a cam-actuated writing element. The writing instrument includes a barrel having a channel therein for receiving a writing element and a cam member coupled to the barrel. The cam member is rotatable between a first position in which a writing end of the writing element is retracted in the channel and a second position in which the writing end of the writing element is extended out of the channel. The cam member rotates about an axis that is substantially transverse to the longitudinal axis of the writing instrument and/or the direction of movement of the writing element. A biasing element may be associated with the writing element for biasing the writing element toward the cam member such that the non-writing end contacts the camming surface. When the cam member is rotated a predetermined distance away from the second position and toward the first position, the biasing element biases the non-writing end of the writing element toward the camming surface and causes the cam member to rotate to the first position independent of the initial rotational force applied to the cam member. The writing instrument may also include a cam follower disposed in the barrel between the cam and the writing element.
According to one aspect of the invention, the barrel includes a cam housing that encloses the cam member such that the camming surface is protected from the environment and contaminants. The cam member may include first and second sides flanking the camming surface and an axle extending from the first and second sides. An actuator member may be located externally to the cam housing and coupled, through the cam housing, to the sides of the cam member, such that the cam member remains enclosed in and protected by the cam housing.
According to another aspect of the invention, the actuator member may conform to the shape of the barrel and remain adjacent thereto throughout movement of the cam member between the first and second positions. The actuator member may include first and second leg portions flanking the cam member. For instance, the actuator member may be U-shaped. The cam member thus may rotate in a first plane with portions of the actuator member rotating in a second plane substantially parallel to the first plane.
According to yet another aspect of the invention, the cam member may include an arcuate camming surface having first and second neutral portions for receiving an end of the writing element or a cam follower (either being referenced as xe2x80x9cthe driven elementxe2x80x9d). Such a camming surface may optionally include a track for receiving and holding in proper alignment the end of the driven element, and may also be polished to decrease friction between the camming surface and the end of the driven element. The camming surface gradually transitions from the first neutral portion to the second neutral portion and is free of any sharp edges or angles. The cam member defines an axis of rotation and a radial distance from the axis of rotation to the camming surface. The radial distance gradually increases in a direction away from the first neutral portion toward the second neutral portion such that movement of the cam member with respect to the writing element effects a smooth transition of the writing element between a retracted position and an extended position.
Finally, according to one more aspect of the invention, the writing instrument may be configured to facilitate replacement or interchanging of the writing element. For instance, the interior channel in the barrel may be configured and dimensioned such that upon accessing and removing the writing element, the cam and, if provided, the cam follower as well are blocked from sliding out of the barrel and do not inadvertently fall out of the barrel.